As conventional spectral modules, those described in Patent Literatures 1 to 3 have been known, for example. Patent Literature 1 discloses a spectral module comprising a support which transmits light therethrough, an entrance slit for letting the light enter the support, a concave diffraction grating which spectrally resolves and reflects the light having entered the support, and a diode for detecting the light spectrally resolved and reflected by the concave diffraction grating.